Application of the Airborne Electromagnetic Method for Banded Iron-Formation Mapping in the Hamersley Province, Western Australia

Abstract

Stratigraphy of the Hamersley Province in Western Australia, featuring alternating units of banded iron-formations and shales with contrasting electrical properties in a mostly gently undulating shallow dipping layered geometry, is particularly favourable to airborne time-domain electromagnetic mapping techniques. Manipulated vertical cross-sections of modelled conductivity obtained from laterally constrained 1D inversion of SkyTEM304 data enable the exploration geologist to interpret weathering profiles, shallow dipping stratigraphy and steep structures, all of which are crucial aspects of bedded iron ore deposits genesis models. Five potential interpretation pitfalls have nevertheless been encountered. Occasional obvious artefacts can be present in inverted models but their causative sources should be easily identifiable in the measured channel data. The inverted models coherence is generally compromised when acquisition system terrain clearance cannot be maintained below approximately 80 m. The in-loop setup and processing routines have inherent limitations over steep stratigraphy. Complex stratigraphy geometries can result in off line responses to be artificially incorporated in the 1D inverted conductivity cross-sections. Lastly, lateral interfaces between fresh and altered rocks could easily be misinterpreted as fault contacts.